yet another riddle

[EngenZerO]

Assume you have 9 identical looking balls. 1 out of those 9 balls equals the weight of the other eight balls. Your task is to find that 1 ball that equals the weight of the other eight balls.

The only tool you are allowed to use is a balance scale to help you determine that 1 heavy ball.

Assume that all nine balls are off the scale in the beginning

1 try is considered placing any number of balls on this balance scale and observing the results. You can add and remove balls in order to help you determine the heaviest.

balls are equal weight (mentioned in post 7)

What is the least number of tries needed to determine the heaviest ball.

the correct answer is further down in this thread

against the rules

"As you pick them up and put them on the balance for the first time, 1 ball will be friggin heavy compared to the other 8. Mark an 'X' on that one with a magic marker, and go have some lunch."

 

[ohtwell]

Wait, if they are identical, then how could one weigh any more than the others?

NM! It says "identical looking". I'm dumb!



: ) Amanda

 

[lozina]

3 tries is the least possible

1 step: put 5 on one side of scale, 4 on the other
2 step: if the sidewith 4 is heavier, remove 2 of them and move them to the other side
3 step: if the side with 2 balls is heavier, remove one to other side, and the result will tell you heaviest ball

 

[stephenw22]

1

As you pick them up and put them on the balance for the first time, 1 ball will be friggin heavy compared to the other 8. Mark an 'X' on that one with a magic marker, and go have some lunch.

 

[EngenZerO]

Originally posted by: stephenw22
1

As you pick them up and put them on the balance for the first time, 1 ball will be friggin heavy compared to the other 8. Mark an 'X' on that one with a magic marker, and go have some lunch.

well... yeah... but... lets say thats against the rules

 

[Furyline]

Are the other 8 balls equal in weight? Or do they vary? Like do they all weigh 1 lb and then the heavy one is 8 lbs?

 

[Jeraden]

nm, I was assuming it was a scale that gave you a weight, missed the part about it being a balance scale.

 

[EngenZerO]

Originally posted by: Furyline
Are the other 8 balls equal in weight? Or do they vary? Like do they all weigh 1 lb and then the heavy one is 8 lbs?

they are equal wieght.

 

[Sundog]

Originally posted by: stephenw22
1

As you pick them up and put them on the balance for the first time, 1 ball will be friggin heavy compared to the other 8. Mark an 'X' on that one with a magic marker, and go have some lunch.

:thumbsup:

 

[EngenZerO]

Originally posted by: Jeraden
I'm guessing 4.

split into 3 groups of 3.
Takes 2 weighing to determine which group of 3 is heaviest.
Put the first group on, record weight.
Put 2nd group on
- if its same as first weight, the 3rd group is the heaviest
- if its heavier, its the heaviest
- if its lighter, first group is the heaviest

Then you have it down to 3 balls.
Takes 2 weighings there to determine which the heaviest is using same method as above.

close but no

you do not have to weight one ball at a time, you can have multiple balls on the scale.

 

[3chordcharlie]

weigh 4 on each side.

If the weights are equal, you're done.

Otherwise, you split the heavier group into pairs, and again into singles.

three tries, maximum.

 

[BRObedoza]

same as he said *point up*
3

4 on each side, if they're balanced, the last one is the heavier
if one side is heavier, put two on each side, take the heavier side, and split em up again

 

[EngenZerO]

Originally posted by: lozina
3 tries is the least possible

1 step: put 5 on one side of scale, 4 on the other
2 step: if the sidewith 4 is heavier, remove 2 of them and move them to the other side
3 step: if the side with 2 balls is heavier, remove one to other side, and the result will tell you heaviest ball

no. think a little deeper about it

 

[HomeBrewerDude]

here is a solution for three weighs.

split into 4 vs 4

then split the heavies into 2 vs 2

then split the heavies into 1 vs 1

 

[Kev]

This is a trick question. If you have 9 balls the first thing you want to do is go to a doctor and have that checked out. Then worry about weighing them.

 

[EngenZerO]

Originally posted by: HomeBrewerDude
here is a solution for three weighs.

split into 4 vs 4

then split the heavies into 2 vs 2

then split the heavies into 1 vs 1

no, think about it a little more

 

[stephenw22]

Originally posted by: EngenZerO

Originally posted by: stephenw22
1

As you pick them up and put them on the balance for the first time, 1 ball will be friggin heavy compared to the other 8. Mark an 'X' on that one with a magic marker, and go have some lunch.

well... yeah... but... lets say thats against the rules

Okay then, my answer is 2.

You take two groups of 3 and balance them on the scale. If it balances then the heavy one is in the group you didn't put on. If not keep the heavy group and toss the rest.

Then take 2 out of the heavy 3 group and balance them. If it balances, then the heavy one is the one that you didn't weigh. Otherwise, it's the heavy one.

 

[EngenZerO]

Originally posted by: stephenw22

Originally posted by: EngenZerO

Originally posted by: stephenw22
1

As you pick them up and put them on the balance for the first time, 1 ball will be friggin heavy compared to the other 8. Mark an 'X' on that one with a magic marker, and go have some lunch.

well... yeah... but... lets say thats against the rules

Okay then, my answer is 2.

You take two groups of 3 and balance them on the scale. If it balances then the heavy one is in the group you didn't put on. If not keep the heavy group and toss the rest.

Then take 2 out of the heavy 3 group and balance them. If it balances, then the heavy one is the one that you didn't weigh. Otherwise, it's the heavy one.

bingo

 

[lozina]

trick question- you cannot put balls on a scale because they'll just roll off

 

[stephenw22]

Originally posted by: lozina
trick question- you cannot put balls on a scale because they'll just roll off

:thumbsup:

 

[lozina]

Originally posted by: EngenZerO

Originally posted by: stephenw22

Originally posted by: EngenZerO

Originally posted by: stephenw22
1

As you pick them up and put them on the balance for the first time, 1 ball will be friggin heavy compared to the other 8. Mark an 'X' on that one with a magic marker, and go have some lunch.

well... yeah... but... lets say thats against the rules

Okay then, my answer is 2.

You take two groups of 3 and balance them on the scale. If it balances then the heavy one is in the group you didn't put on. If not keep the heavy group and toss the rest.

Then take 2 out of the heavy 3 group and balance them. If it balances, then the heavy one is the one that you didn't weigh. Otherwise, it's the heavy one.

bingo

this assumes the other 8 balls are equal weight, information which was not disclosed to us

 

[stephenw22]

Originally posted by: lozina

Originally posted by: EngenZerO

Originally posted by: stephenw22

Originally posted by: EngenZerO

Originally posted by: stephenw22
1

As you pick them up and put them on the balance for the first time, 1 ball will be friggin heavy compared to the other 8. Mark an 'X' on that one with a magic marker, and go have some lunch.

well... yeah... but... lets say thats against the rules

Okay then, my answer is 2.

You take two groups of 3 and balance them on the scale. If it balances then the heavy one is in the group you didn't put on. If not keep the heavy group and toss the rest.

Then take 2 out of the heavy 3 group and balance them. If it balances, then the heavy one is the one that you didn't weigh. Otherwise, it's the heavy one.

bingo

this assumes the other 8 balls are equal weight, information which was not disclosed to us

Then my first answer should be the right one.

 

[Mathlete]

Are you sure you can do it in less than three??? That is all I can come up with.

First Weighing

5 on one side four on other

If 4 are heavier than five...

Split into 2 and 2, weigh.

Split the heavier side into 1 and 1

If five are heavier than four

Split into 2 and 3 and weigh

If two are heavier see above

If three are heavier put one on each side. The heavier one will show. If they are the same it is the one that you didn't put on there.

 

[EngenZerO]

Originally posted by: EngenZerO

Originally posted by: Furyline
Are the other 8 balls equal in weight? Or do they vary? Like do they all weigh 1 lb and then the heavy one is 8 lbs?

they are equal wieght.

someone asked, i just didnt re-edit my orginal post

 

[lozina]

Originally posted by: EngenZerO

Originally posted by: EngenZerO

Originally posted by: Furyline
Are the other 8 balls equal in weight? Or do they vary? Like do they all weigh 1 lb and then the heavy one is 8 lbs?

they are equal wieght.

someone asked, i just didnt re-edit my orginal post

Ah ok, I didn't see that